btw I've been doing some searches on this and found a lot of contradictory information on whether or not to raise or lower timing to get rid of the low rpm/low KPA surge. My guess is a lot depends on the cam size. Mine is 220/226/112+6/.544/.544 so it's pretty mild as far as duration goes anyway. Some say higher, some say lower I guess it's whatever works (neither for me so far).

I read something new today that I haven't tried though:

Setting timing to be the same in the cells around the surge. Duh, this makes sense why didn't I think of it sooner? This way when it surges it won't be exacerbated by being sent to another rate of timing in neighboring KPA/RPM cells ...it will still move to those cells but won't be forced to another rate of advance.

 

you really shouldnt have that much of an issue with that size cam.


but anyway, i raised the timing a decent amount and it made a hell of a difference. just do it in small amounts and watch your knock and map sensor. the lower the map sensor get the more efficient your motor is, the better mine drove.

 

The only variables you can control to overcome cam surge is the timing changes and your driving technique... learn how to say out of the surge. Open loop can also help but its not as efficient because you need a wideband O2 sensor and hundreds of hours logging data in order to adjust the fuel delivery.

Something else I have done to eliminate off idle surge was run PE idle to allow me the control of fuel at idle. This is a huge advantage for guys with wide BLM splits.

 

Well, just to experiment to determine whether or not it is fuel related or spark related I disabled closed loop today. The surge is all but GONE ...literally like 95% of it is gone, it drives almost like stock! Everything is better and I mean everything ...idles smooth and no longer has the tendency to want to stall when letting out clutch, upon upshifting it is much smoother going into the next gear, steady cruise is now nice and steady ....real steady and you can barely even tell there's a cam in it. Throttle response is just as good or better. Even though I'm running rich (.910 - .950) just the fact that it's not surging and that I'm not throttling or unthrottliing to avoid the surge probably offsets the difference in MPG. Being an M6 car it seems soooooooo much easier on the drivetrain too. It's just easier and way more pleasurable to drive ....I don't have to "plan" how to pull into my driveway to avoid bucking surge for example.

So now I know for sure it's fuel related, and damn tempted to just leave this thing in open loop. If I do, rather than spending hours upon hours trying to tune it perfectly on a wideband dyno .....I honestly think I could get away with open loop just by leaning out the MAF table a bit in the AFGS where I cruise so it's not so pig rich all the time. My VE tables are already altered considerably from stock to more appropriately match this cam....but IMO they don't get used anyway as long as the MAF is working. My cruise rpm and AFGS is very very limited anyway because I'm generally a super smooth driver and stay in a 1200-1800 rpm and 30-70 KPA range most of the time. I'm either driving it like that (mostly) ....or giving it some hell, during which time it isn't in closed loop anyway; so there's not much inbetween, or in other words ....less reason to really need to keep closed loop. **** we all know closed loop idle is ridiculously rich anyway, so there's another plus ...I wouldn't be dealing with that either!

I will re-enable closed loop anyway and try one or two more tunes with richened MAF to lock my BLM's at 108 in the AFGS areas where I cruise. If that doesn't work to hell with it, I will go to open loop and lean out the MAF some in those same AFGS areas.

Back when I had this thing wideband dyno tuned when it was a stock engine w/blower & headers ... and the tuner wound up disabling closed loop. I ran it in that configuration without any problems and had great MPG even while seeing .900+ mv's on my Scanmaster at light throttle. It didn't foul plugs or pour out black smoke either. I'm thinking ....since I know from experience that ~.900 cruise is ok to see in open loop maybe I'll just shoot for that or a tad leaner via my MAF adjustments. I won't adjust the whole table, just the AFGS areas where I cruise, then feather in neighboring AFGS gradually back to stock.

Does my logic sound reasonable or should I try my heart out at tuning it with closed loop enabled? I just fear that will take a lot more effort as far as surge reduction goes and not be worth the time spent anyway. BTW, this is not a daily driver ...so even less need for closed loop.